This invention relates to a process in which a powder is produced by forming an aqueous solution including precursors of the powder material, mixing to emulsify the aqueous solution in a water-immiscible fluid, and drying and separating the emulsion droplets.
Ceramic materials are made by the thermal decomposition of metal organic resins. Such a method is described by M. Pechini in his U.S. Pat. No. 3,330,697 issued July 11, 1957, and assigned to the same assignee as is the present invention. This method provides highly homogeneous bulk material but not powder.
Finely divided ceramic materials have been made by emulsifying an aqueous solution of a metal salt in a water-immiscible liquid. The water of the emulsion is then evaporated without boiling away a significant part of the water-immiscible fluid, and the emulsion is transformed into a metal-salt sol. Subsequently, the sol is caused to coagulate (flocculate) e.g., by heating and/or by the addition of a propanol, ethanol, or the like. The heating is also for simultaneously thermally decomposing the metal salt to produce a refractory powder.
Another method, dedicated to making alkali-earth-metal titanate powders, begins by forming alcoholates of each of the precursor metals, mixing the alcoholates and refluxing the mixture, adding water to the mixture to form a precipitate, separating the precipitate from the solution and drying the recovered titanate powder.
The later two processes, by which particles of metal compounds are separated by precipitation from a solution, are capable of producing fine powders, but inevitably some of the fine particles so produced agglomerate to form large particles.
It is therefore an object of this invention to provide a method for making a finely divided powder of a wide range of compositions.
It is a further object of this invention to provide such a method wherein initially the powder product precursors are dissolved in an aqueous solution that is emulsified to establish the ultimate sizes of the final powder particles.
It is yet a further object of this invention to provide such a method wherein the emulsion is subjected to drying to form a dispersion and heating the dispersion in an essentially inert atmosphere to char the dispersion whereby the carbon in the char maintains separation of the dried particles.